Folded cascode amplifiers are typically used to obtain reasonable common mode and output range in low power supply voltage applications. A folded cascode amplifier is an arrangement of active electronic devices that combines an input stage and a folded cascode load stage to increase gain for increased output resistance and reduced parasitic capacitance, resulting in high gain with increased bandwidth. Quiescent current is the current that flows in the folded cascode amplifier stage during small signal amplifier operation. When there are relatively large voltage changes between the amplifier inputs (e.g., during large signal amplifier operation) there is a corresponding change in the amplifier output. The nonlinear effect of these changes is termed slewing and the slew rate is the maximum rate of change of signal at an amplifier output. It is desirable to maximize the slew rate of the amplifier for many applications. The quiescent current of the folded cascode amplifier stage is typically slightly larger than the input pair tail current on the amplifier inputs to insure a good slew rate.
When the folded cascode amplifier is operated in small signal mode, which does not result in slewing, the larger quiescent current in the folded cascode stage wastes power. Moreover, a larger quiescent current in the folded cascode stage also provides higher noise. However, in order to maintain smooth slew transition, the quiescent current must be sufficiently high.